// Create a client
AmazonDynamoDBClient client = new AmazonDynamoDBClient();

// Define item key
//  Hash-key of the target item is string value "Mark Twain"
//  Range-key of the target item is string value "The Adventures of Tom Sawyer"
Key key = new Key
{
    HashKeyElement = new AttributeValue { S = "Mark Twain" },
    RangeKeyElement = new AttributeValue { S = "The Adventures of Tom Sawyer" }
};

// Define attribute updates
Dictionary<string, AttributeValueUpdate> updates = new Dictionary<string, AttributeValueUpdate>();
// Update item's Setting attribute
updates["Setting"] = new AttributeValueUpdate()
    .WithAction("PUT")
    .WithValue(new AttributeValue { S = "St. Petersburg, Missouri" });
// Remove item's Bibliography attribute
updates["Bibliography"] = new AttributeValueUpdate()
    .WithAction("DELETE");
// Add a new string to the item's Genres SS attribute
updates["Genres"] = new AttributeValueUpdate()
    .WithAction("ADD")
    .WithValue(new AttributeValue { SS = new List<string> { "Bildungsroman" } });

// Create UpdateItem request
UpdateItemRequest request = new UpdateItemRequest
{
    TableName = "SampleTable",
    Key = key,
    AttributeUpdates = updates
};

// Issue request
client.UpdateItem(request);